White light emitting device and white light source module using the same

ABSTRACT

A white light emitting device including: a blue light emitting diode chip having a dominant wavelength of 443 to 455 nm; a red phosphor disposed around the blue light emitting diode chip, the red phosphor excited by the blue light emitting diode chip to emit red light; and a green phosphor disposed around the blue light emitting diode chip, the green phosphor excited by the blue light emitting diode chip to emit green light, wherein the red light emitted from the red phosphor has a color coordinate falling within a space defined by four coordinate points (0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) based on the CIE 1931 chromaticity diagram, and the green light emitted from the green phosphor has a color coordinate falling within a space defined by four coordinate points (0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE 1931 color chromaticity diagram.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application Nos.2006-122631 filed on Dec. 5, 2007 and 2007-12112 filed on Feb. 6, 2007,in the Korean Intellectual Property Office, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a white light emitting device and awhite light source module using the same, and more particularly, to awhite light emitting device beneficially applicable to a backlight unitof a liquid crystal display to ensure high color reproducibility, and awhite light source module using the same.

2. Description of the Related Art

Recently, a light emitting diode (LED) is highlighted as a light sourceof a backlight unit (BLU) employed in liquid crystal displays such aslap top computers, monitors, mobile phones and TVs. A cold cathodefluorescent lamp (CCFL) has been in use as a white light source of theBLU, but lately, a white light source module using the LED has capturedattention due to its advantages such as better color representation,environment friendliness, higher performance and lower powerconsumption.

In a conventional white light source module for the BLU, a blue LED, agreen LED and a red LED are arranged on a circuit board. FIG. 1illustrates an example of such arrangement. Referring to FIG. 1, a whitelight source module 10 for a BLU includes a red R LED 12, a green G LED14 and a blue LED 16 arranged on a circuit board 11 such as a printedcircuit board. The R, G, and B LEDs 12, 14, and 16 may be mounted on theboard 11 in a configuration of packages each including an LED chip of acorresponding color, or lamps. These R, G, and B LED packages or lampsmay be repeatedly arranged on the board to form an overall white surfaceor line light source. As described above, the white light source module10 employing the R, G, and B LEDs is relatively excellent in colorreproducibility and an overall output light can be controlled byadjusting a light amount of the R, G, and B LEDs.

However, in the white light source module 10 described above, the R, G,and B LEDs 12, 14, and 16 are spaced apart from another, therebypotentially posing a problem to color uniformity. Moreover, to producewhite light of a unit area, at least a set of R, G, and B LED chips isrequired since the three-colored LED chips constitute a white lightemitting device. This entails complicated circuit configuration fordriving and controlling the LED of each color, thus leading to highercosts for circuits. This also increases the manufacturing costs forpackages and the number of the LEDs required.

Alternatively, to implement a white light source module, a white lightemitting device having a blue LED and a yellow phosphor has beenemployed. The white light source module utilizing a combination of theblue LED and yellow phosphor is simple in circuit configuration and lowin price. However, the white light source module is poor in colorreproducibility due to relatively low light intensity at a longwavelength. Therefore, a higher-quality and lower-cost LCD requires awhite light emitting device capable of assuring better colorreproducibility, and a white light source module using the same.

Accordingly, there has been a call for maximum color reproducibility andstable color uniformity of the white light emitting device adopting theLED and phosphor, and the white light source module using the same.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a white light emittingdevice with high color reproducibility and superior color uniformity.

An aspect of the present invention also provides a white light sourcemodule with high color reproducibility and superior color uniformity,which is manufactured with lower costs.

According to an aspect of the present invention, there is provided awhite light emitting device including: a blue light emitting diode (LED)chip having a dominant wavelength of 443 to 455 nm; a red phosphordisposed around the blue LED chip, the red phosphor excited by the blueLED chip to emit red light; and a green phosphor disposed around theblue LED chip, the green phosphor excited by the blue LED chip to emitgreen light, wherein the red light emitted from the red phosphor has acolor coordinate falling within a space defined by four coordinatepoints (0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794,0.4633) based on the CIE 1931 chromaticity diagram, and the green lightemitted from the green phosphor has a color coordinate falling within aspace defined by four coordinate points (0.1270, 0.8037), (0.4117,0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE 1931color chromaticity diagram.

The blue LED chip may have a full width at half-maximum (FWHM) of 10 to30 nm , the green phosphor may have a FWHM of 30 to 100 nm and the redphosphor may have a FWHM of 50 to 200 nm. The red phosphor may includeat least one of CaAlSiN₃:Eu and (Ca,Sr)S:Eu. The green phosphor mayinclude at least one of A₂SiO₄:Eu, SrGa₂S₄:Eu and β-SiAlON, wherein A inA₂SiO₄:Eu is at least one of Ba, Sr and Ca.

The white light emitting device may further include a resin encapsulantencapsulating the blue LED chip, wherein the green phosphor and the redphosphor are dispersed in the resin encapsulant.

The white light emitting device may further include a resin encapsulantencapsulating the blue LED chip, wherein a first phosphor film includingone of the green and red phosphors is formed along a surface of the blueLED chip between the green light emitting device chip and the resinencapsulant, and a second phosphor film including the other one of thegreen and red phosphors is formed on the resin encapsulant.

According to another aspect of the present invention, there is provideda white light source module including: a circuit board; a blue LED chipdisposed on the circuit board and having a dominant wavelength of 443 to455 nm; a red phosphor disposed around the blue LED chip, the redphosphor excited by the blue LED chip to emit red light; and a greenphosphor disposed around the blue LED chip, the green phosphor excitedby the blue LED chip to emit green light, wherein the red light emittedfrom the red phosphor has a color coordinate falling within a spacedefined by four coordinate points (0.5448, 0.4544), (0.7079, 0.2920),(0.6427, 0.2905) and (0.4794, 0.4633) based on the CIE 1931 colorchromaticity diagram, and the green light emitted from the greenphosphor has a color coordinate falling within a space defined by fourcoordinate points (0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316)and (0.2555, 0.5030) based on the CIE 1931 color chromaticity diagram.

The blue LED chip may have a FWHM of 10 to 30 nm, the green phosphor mayhave a FWHM of 30 to 100 nm and the red phosphor may have a FWHM of 50to 200 nm. The red phosphor may include at least one of CaAlSiN₃:Eu and(Ca,Sr)S:Eu. The green phosphor may include at least one of A₂SiO₄:Eu,SrGa₂S₄:Eu and β-SiAlON, wherein A in A₂SiO₄:Eu is at least one of Ba,Sr and Ca.

The white light source module may further include a resin encapsulantencapsulating the blue LED chip, wherein the blue LED chip is directlymounted on the circuit board.

The white light source module may further include a package body mountedon the circuit board, the package body defining a reflective cup,wherein the blue LED chip is mounted in the reflective cup defined bythe package body.

The white light source module may further include a resin encapsulantformed inside the reflective cup defined by the package body, theencapsulant encapsulating the blue LED chip.

The white light source module may further include a resin encapsulantencapsulating the blue LED chip, wherein the green phosphor and the redphosphor are dispersed in the resin encapsulant.

The white light source module may further include a resin encapsulantencapsulating the blue light emitting device chip, wherein a firstphosphor film including one of the green and red phosphors is formedalong a surface of the blue LED chip between the blue light emittingdiode chip and the resin encapsulant, and a second phosphor filmincluding the other one of the green and red phosphors is formed on theresin encapsulant.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a cross-sectional view illustrating a conventional white lightsource module for a backlight unit;

FIG. 2 is a cross-sectional view illustrating a white light emittingdevice and a white light source module according to an exemplaryembodiment of the invention;

FIG. 3 is a cross-sectional view illustrating a white light emittingdevice and a white light source module according to an exemplaryembodiment of the invention;

FIG. 4 is a cross-sectional view illustrating a white light emittingdevice and a white light source module according to an exemplaryembodiment of the invention;

FIG. 5 is a cross-sectional view illustrating a white light emittingdevice and a white light source module according to an exemplaryembodiment of the invention;

FIG. 6 illustrates a color coordinate space of phosphors used in a whitelight emitting device according to an exemplary embodiment of theinvention; and

FIG. 7 illustrates a color coordinate range obtained in a case wherewhite light source modules of Inventive Example and Comparative Exampleare employed in a backlight unit of a liquid crystal display (LCD).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the shapes and dimensions may beexaggerated for clarity, and the same reference signs are used todesignate the same or similar components throughout.

FIG. 2 is a schematic cross-sectional view illustrating a white lightemitting device and a white light source module using the same accordingto an exemplary embodiment of the invention. Referring to FIG. 2, thewhite light source module 510 includes a circuit board 101 such as aprinted circuit board, and at least one white light emitting device 100disposed on the circuit board 101. The white light emitting device 100includes a blue B light emitting diode (LED) chip 103, a green Gphosphor 105 and a red R phosphor 107. The green phosphor 105 and thered phosphor 107 are excited by the blue LED chip 103 to emit greenlight and red light, respectively. The green light and the red light aremixed with a portion of the blue light from the blue LED chip 103 toproduce white light.

Particularly, according to the present embodiment, the blue LED chip 103is directly mounted on the circuit board 101 and the phosphors 105 and107 are dispersed and mixed uniformly in a resin encapsulant 130encapsulating the blue LED chip 103. The resin encapsulant 130 may beformed, for example, in a semi-circle which serves as a kind of lens.Alternatively, the resin encapsulant 130 may be formed of one of anepoxy resin, a silicone resin and a hybrid resin. As described above,the blue LED chip 103 is directly mounted on the circuit board 101 by achip-on-board technique, thereby allowing the white light emittingdevice 100 to achieve a greater view angle more easily.

One of an electrode pattern and a circuit pattern (not shown) is formedon the circuit board 101, and the circuit pattern is connected to anelectrode of the blue LED chip 103 by e.g., wire bonding or flip chipbonding. This white light source module 510 may include a plurality ofthe white light emitting devices 100 to form a surface or line lightsource with a desired area, thereby beneficially utilized as a lightsource of a backlight unit of the LCD device.

The inventors of the present invention have defined a dominantwavelength of the blue LED chip 103 to be in a specific range and acolor coordinate of the red and green phosphors 105 and 107 to be withina specific space based on the CIE 1931 color chromaticity diagram. Thisenabled the inventors to realize maximum color reproducibility from acombination of the green and red phosphors and the blue LED chip.

Specifically, to obtain maximum color reproducibility from a combinationof the blue LED chip-green phosphor-red phosphor, the blue LED chip 103has a dominant wavelength of 443 to 455 nm. Also, the red light emittedfrom the red phosphor 107 excited by the blue LED chip 103 has a colorcoordinate falling within a space defined by four coordinate points(0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794,0.4633) based on the CIE 1931 (x, y) color chromaticity diagram.Moreover, the green light emitted from the green phosphor excited by theblue LED chip 103 has a color coordinate falling within a space definedby (0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316) and (0.2555,0.5030) based on the CIE 1931 color chromaticity diagram.

FIG. 6 illustrates color coordinate spaces of the red and greenphosphors described above. Referring to FIG. 6, the CIE 1931 colorchromaticity diagram is marked with a quadrilateral-shaped spacercomposed of four coordinate points (0.5448, 0.4544), (0.7079, 0.2920),(0.6427, 0.2905) and (0.4794, 0.4633) and a quadrilateral-shaped space gcomposed of four coordinate points (0.1270, 0.8037), (0.4117, 0.5861),(0.4197, 0.5316) and (0.2555, 0.5030). As described above, the redphosphor and green phosphor are selected such that color coordinatesthereof fall within the quadrilateral-shaped spaces r and g,respectively.

Here, a dominant wavelength is a wavelength value derived from a curveobtained by integrating an actually-measured spectrum graph of an outputlight of the blue LED chip and a luminosity curve. The dominantwavelength is a value considering visibility of a person. This dominantwavelength corresponds to a wavelength value at a point where a lineconnecting a center point (0.333, 0.333) of the CIE 1976 colorchromaticity diagram to the actually-measured color coordinate meets acontour line of the CIE 1976 chromaticity diagram. It should be notedthat a peak wavelength is different from the dominant wavelength. Thepeak wavelength has the highest energy intensity. The peak wavelength isa wavelength value indicating the highest intensity in the spectrumgraph of the actually-measured output light, regardless of luminosity.

Here, the blue LED chip 103 has a dominant wavelength of 443 to 455 nm.The red phosphor 107 has a color coordinate falling within aquadrilateral space defined by four coordinate points (0.5448, 0.4544),(0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633), based on theCIE 1931 color chromaticity diagram. The green phosphor 105 has a colorcoordinate falling within a quadrilateral space defined by fourcoordinate points (0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316)and (0.2555, 0.5030). Accordingly, a liquid crystal display (LCD) deviceemploying the white light source module 510 for a backlight unit mayexhibit high color reproducibility across a very large color coordinatespace covering a substantially entire s-RGB space on the CIE 1976chromaticity diagram (see FIG. 7). This high color reproducibility ishardly attainable from a conventional combination of a blue LED chip andred and green phosphors.

The blue LED chip and red and green phosphors falling outside thedominant wavelength range and color coordinate space as described abovemay degrade color reproducibility or color quality of the LCD.Conventionally, the blue LED chip used along with the red and greenphosphors to obtain white light has a dominant wavelength of typically460 nm or more. However, according to the present embodiment, the bluelight has a shorter dominant wavelength than the conventional one andthe red and green phosphors have a color coordinate falling within thequadrilateral space as described above, thereby producing higher colorreproducibility which is hardly achieved by the prior art.

The blue LED chip 103 may adopt a group-III nitride semiconductor LEDdevice in general use. Also, the red phosphor 107 may utilize a nitridephosphor such as CaAlSiN₃:Eu. This nitride red phosphor is lessvulnerable to the external environment such as heat and moisture than ayellow phosphor, and less likely to be discolored. Notably, the nitridered phosphor exhibits high excitation efficiency with respect to theblue LED chip having a dominant wavelength set to a specific range of443 to 455 nm to obtain high color reproducibility. Other nitridephosphors such as Ca₂Si₅N₈:Eu or the yellow phosphor such as (Ca,Sr)S:Eumay be utilized as the red phosphor 107. The green phosphor 105 mayadopt a silicate phosphor such as A₂SiO₄:Eu where A is at least one ofBa, Sr and Ca. For example, the green phosphor 105 may employ(Ba,Sr)₂SiO₄:Eu. The silicate phosphor demonstrates high excitationefficiency with respect to the blue LED chip having a dominantwavelength of 443 to 455 nm. Alternatively, one of SrGa₂S₄:Eu andβ-SiAlON (Beta-SiAlON) may be utilized as the green phosphor 105.

Particularly, the blue LED chip 103 has a full width at half maximum(FWHM) of 10 to 30 nm, the green phosphor 105 has a FWHM of 30 to 100nm, and the red phosphor 107 has a FWHM of 50 to 200 nm. The lightsources 103, 105, and 107 with the FWHM ranging as described aboveproduces white light of better color uniformity and higher colorquality. Especially, the blue LED chip 103 having a dominant wavelengthof 443 to 455 nm and a FWHM of 10 to 30 nm significantly enhancesexcitation efficiency of the CaAlSiN₃:Eu or (Ca,Sr)S:Eu red phosphor andthe A₂SiO₄:Eu, SrGa₂S₄:Eu, or β-SiAlON green phosphor. Here, A inA₂SiO₄:Eu is at least one of Ba, Sr, and Ca.

According to the present embodiment, the blue LED chip has a dominantwavelength of a predetermined range and the green and red phosphors havecolor coordinates within a predetermined space. This allows superiorcolor reproducibility than a conventional combination of the blue LEDchip and yellow phosphor, and than a conventional combination of theblue LED chip and green and red phosphors, respectively. This alsoimproves excitation efficiency and overall light efficiency as well.

Furthermore, according to the present embodiment, unlike theconventional white light source module using the red, green and blue LEDchips, a fewer number of LED chips are required and only one type of theLED chip, i.e., blue LED chip is required. This accordingly reducesmanufacturing costs for packages and simplifies a driving circuit.Notably, an additional circuit may be configured with relativesimplicity to increase contrast or prevent blurring. Also, only one LEDchip 103 and the resin encapsulant encapsulating the LED chip 103 allowwhite light of a unit area to be emitted, thereby ensuring superiorcolor uniformity to a case where the red, green and blue LED chips areemployed.

FIG. 3 is schematic cross-sectional view illustrating a white lightemitting device 200 and a white light source module 520 using the same.In the embodiment of FIG. 3, a blue LED chip 103 is directly mounted ona circuit board 101 by a chip-on-board technique. The blue LED chip 103constitutes the white light emitting device 200 of a unit area togetherwith a red phosphor and a green phosphor excited by the blue LED chip103. Moreover, to achieve maximum color reproducibility, the blue LEDchip 103 has a dominant wavelength range, and the red phosphor and greenphosphor have a color coordinate space as described above, respectively.That is, the blue LED chip 103 has a dominant wavelength of 443 to 455nm. The red phosphor has a color coordinate falling within aquadrilateral space defined by four coordinate points (0.5448, 0.4544),(0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) on the CIE 1931color chromaticity diagram. The green phosphor has a color coordinatefalling within a quadrilateral space defined by four coordinate points(0.1270, 0.8037), (0.4117, 0.5861), (0.4197, 0.5316) and (0.2555,0.5030).

However, according to the present embodiment, the red and greenphosphors are not dispersed and mixed in a resin encapsulant butprovided as a phosphor film. Specifically, as shown in FIG. 3, a greenphosphor film 205 containing the green phosphor is thinly applied alonga surface of the blue LED chip 103 and a semi-circular transparent resinencapsulant 230 is formed on the green phosphor film 205. Also, a redphosphor film 207 containing the red phosphor is applied on a surface ofthe transparent resin encapulant 230. The green phosphor film 205 andthe red phosphor film 207 may be located reversely with each other. Thatis, the red phosphor film 207 may be applied on the blue LED chip 103and the green phosphor film 205 may be applied on the resin encapsulant230. The green phosphor film 205 and the red phosphor film 207 may beformed of a resin containing green phosphor particles and red phosphorparticles, respectively. The phosphors contained in the phosphor films207 and 205 may employ one of a nitride, a yellow phosphor and asilicate phosphor as described above.

As described above, in the white light emitting device 200, the greenphosphor film 205, the transparent resin encapsulant 230, and the redphosphor film 207 are formed to further enhance color uniformity ofwhite light outputted. When the green and red phosphors (powder mixture)are merely dispersed in the resin encapsulant, the phosphors are notuniformly distributed due to difference in weight between the phosphorsduring resin curing, thus risking a problem of layering. This may reducecolor uniformity in a single white light emitting device. However, in acase where the green phosphor film 205 and the red phosphor film 207separated by the resin encapsulant 230 are adopted, the blue lightemitted at various angles from the blue LED chip 103 are relativelyuniformly absorbed or transmitted through the phosphor films 205 and207, thereby producing more uniform white light overall. That is, coloruniformity is additionally enhanced.

Also, as shown in FIG. 3, the phosphor films 205 and 207 separate fromeach other by the transparent resin encapsulant 230 may lowerphosphor-induced optical loss. In a case where the phosphor powdermixture is dispersed in the resin encapsulant, secondary light (greenlight or red light) wavelength-converted by the phosphor is scattered byphosphor particles present on an optical path, thereby causing opticalloss. However, in the embodiment of FIG. 3, the secondary lightwavelength-converted by the thin green or red phosphor film 205 or 207passes through the transparent resin encapsulant 230 or is emittedoutside the light emitting device 200, thereby lowering optical lossresulting from the phosphor particles.

In the embodiment of FIG. 3, the blue LED chip has a dominant wavelengthrange, and the green and red phosphors have color coordinate space asdescribed above, respectively. Accordingly, the white light sourcemodule 520 for the BLU of the LCD exhibits high color reproducibilityacross a very large space covering a substantially entire S-RGB space.This also reduces the number of the LED chips, and manufacturing costsfor driving circuits and packages, thereby realizing lower unit costs.Of course, the blue, green and red light may have a FWAH ranging asdescribed above.

In the present embodiments described above, each of LED chips isdirectly mounted on the circuit board by a COB technique. However, thepresent invention is not limited thereto. For example, the LED chip maybe mounted inside a package body mounted on the circuit board. FIGS. 4and 5 illustrate additional package bodies employed according to anexemplary embodiment of the invention, respectively.

FIG. 4 is a cross-sectional view illustrating a white light emittingdevice 300 and a white light source module 530 using the same accordingto an exemplary embodiment of the invention. Referring to FIG. 4, apackage body 310 defining a reflective cup is mounted on a circuit board101. A blue B LED chip 103 is disposed on a bottom of the reflective cupdefined by the package body 310 and a resin encapsulant 330 having agreen R phosphor 105 and a red G phosphor 107 dispersed thereinencapsulates the LED chip 103. To attain a surface or line light sourcewith a desired area, a plurality of the white light emitting devices300, i.e., a plurality of the LED packages may be arranged on the board101.

Also in the embodiment of FIG. 4, the blue LED chip has a dominantwavelength range, and the red and green phosphors have color coordinatespaces as described above, respectively, thereby assuring high colorreproducibility. Furthermore, the number of the LED chips, andmanufacturing costs for driving circuits and packages are declined torealize lower unit costs.

FIG. 5 is a schematic cross-sectional view illustrating a white lightemitting device and a white light source module 540 using the sameaccording to an exemplary embodiment of the invention. Referring to FIG.5, as in the embodiment of FIG. 4, the white light emitting device 400includes a package body 410 defining a reflective cup and a blue LEDchip 103 mounted on the reflective cup.

However, according to the present embodiment, the red and greenphosphors are not dispersed and mixed in a resin encapsulant andprovided as a phosphor film. That is, one of a green phosphor 405 and ared phosphor 407 is applied along a surface of the blue LED chip 103 anda transparent resin encapsulant 430 is formed thereon. Also, the otherone of the green and red phosphors 405 and 407 is applied along asurface of the transparent resin encapsulant 430.

As in the embodiment of FIG. 3, in the embodiment of FIG. 5, the greenphosphor film 405 and the red phosphor film 407 separated from eachother by the resin encapsulant 430 are employed to ensure superior coloruniformity. Also, in the same manner as the aforesaid embodiments, theblue LED chip has a dominant wavelength range and the red and greenphosphors have color coordinate spaces as described above, therebyproducing high color reproducibility across a very large space coveringa substantially entire s-RGB space.

FIG. 7 illustrates the CIE 1976 chromatic diagram indicating colorcoordinate ranges obtained in a case where white light source modules ofInventive Example and Comparative Example are employed in BLUs of LCDs,respectively.

Referring to FIG. 7, the white light source module of Inventive Exampleemits white light by a combination of a blue LED chip, a red phosphorand a green phosphor (see FIG. 4). In the white light source ofInventive Example, the blue LED chip has a dominant wavelength of 443 to455 nm, particularly 451 nm. Also, the red phosphor emits red lighthaving a color coordinate falling within a quadrilateral space definedby four coordinate points (0.5448, 0.4544), (0.7079, 0.2920), (0.6427,0.2905) and (0.4794, 0.4633) based on the CIE 1931 color chromaticitydiagram. The green phosphor emits green light having a color coordinatefalling within a quadrilateral space defined by (0.1270, 0.8037),(0.4117, 0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE1931 color chromaticity diagram.

Meanwhile, the white light source module of Comparative Example 1 emitswhite light by a combination of red, green and blue LED chips. Also, awhite light source module of Comparative Example 2 emits white lightusing a conventional cold cathode fluorescent lamp.

The chromaticity diagram of FIG. 7 indicates a color coordinate space ofthe LCD employing the light source module of Inventive Example as theBLU, and a color coordinate space of the LCDs employing the lightsources of Comparative Example land Comparative Example 2 as the BLUs,respectively. As shown in FIG. 7, the LCD adopting the BLU according toInventive Example exhibits a very broad color coordinate space coveringa substantially entire s-RGB space. This high color reproducibility isnot attainable by a conventional combination of a blue LED chip, red andgreen phosphors.

The LCD utilizing the BLU (RGB LED BLUE) according to ComparativeExample 1 employs only the LED chips as red, green and blue lightsources, thus demonstrating a broad color coordinate space. However, asshown in FIG. 7, the LCD adopting the RGB LED BLU according toComparative Example 1 disadvantageously does not exhibit a blue color inthe s-RGB space. Also, only three-color LED chips employed withoutphosphors degrade color uniformity, while increasing the number of theLED chips required and manufacturing costs. Notably, this entailscomplicated configuration of an additional circuit for contrast increaseor local dimming, and drastic increase in costs for the circuitconfiguration.

As shown in FIG. 7, the LCD employing the BLU (CCFL BLU) of ComparativeExample 2 exhibits a relatively narrow color coordinate space, thuslowered in color reproducibility over the BLUs of Inventive Example andComparative Example 1, respectively. Moreover, the CCFL BLU is notenvironment-friendly and can be hardly configured in a circuit forimproving its performance such as local dimming and contrast adjustment.

As set forth above, according to exemplary embodiments of the invention,a blue LED chip having a dominant wavelength of a specific range, andred and green phosphors having a color coordinate of a specific space,respectively, are employed. This assures high color reproducibilitywhich is hardly realized by a conventional combination of a blue LEDchip, red and green phosphors. This also results in superior coloruniformity and reduces the number of the LEDs necessary for a lightsource module for a BLU, and costs for packages and circuitconfiguration. In consequence, this easily produces a higher-quality andlower-cost white light source module and a backlight unit using thesame.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

1. A white light emitting device comprising: a blue light emitting diodechip having a dominant wavelength of 443 to 455 nm; a red phosphordisposed around the blue light emitting diode chip, the red phosphorexcited by the blue light emitting diode chip to emit red light; and agreen phosphor disposed around the blue light emitting diode chip, thegreen phosphor excited by the blue light emitting diode chip to emitgreen light, wherein the red light emitted from the red phosphor has acolor coordinate falling within a space defined by four coordinatepoints (0.5448, 0.4544), (0.7079, 0.2920), (0.6427, 0.2905) and (0.4794,0.4633) based on the CIE 1931 chromaticity diagram, and the green lightemitted from the green phosphor has a color coordinate falling within aspace defined by four coordinate points (0.1270, 0.8037), (0.4117,0.5861), (0.4197, 0.5316) and (0.2555, 0.5030) based on the CIE 1931color chromaticity diagram.
 2. The white light emitting device of claim1, wherein the blue light emitting diode chip has a full width athalf-maximum of 10 to 30 nm, the green phosphor has a full width athalf-maximum of 30 to 100 nm and the red phosphor has a full width athalf-maximum of 50 to 200 nm.
 3. The white light emitting device ofclaim 1, wherein the red phosphor comprises at least one of CaAlSiN₃:Euand (Ca,Sr)S:Eu.
 4. The white light emitting device of claim 1, whereinthe green phosphor comprises at least one of A₂SiO₄:Eu, SrGa₂S₄:Eu andβ-SiAlON, wherein A in A₂SiO₄:Eu comprises at least one of Ba, Sr andCa.
 5. The white light emitting device of claim 1, further comprising aresin encapsulant encapsulating the blue light emitting diode chip,wherein the green phosphor and the red phosphor are dispersed in theresin encapsulant.
 6. The white light emitting device of claim 1,further comprising a resin encapsulant encapsulating the blue lightemitting diode chip, wherein a first phosphor film comprising one of thegreen and red phosphors is formed along a surface of the blue lightemitting diode chip between the green light emitting device chip and theresin encapsulant, and a second phosphor film comprising the other oneof the green and red phosphors is formed on the resin encapsulant.
 7. Awhite light source module comprising: a circuit board; a blue lightemitting diode chip disposed on the circuit board and having a dominantwavelength of 443 to 455 nm; a red phosphor disposed around the bluelight emitting diode chip, the red phosphor excited by the blue lightemitting diode chip to emit red light; and a green phosphor disposedaround the blue light emitting diode chip, the green phosphor excited bythe blue light emitting diode chip to emit green light, wherein the redlight emitted from the red phosphor has a color coordinate fallingwithin a space defined by four coordinate points (0.5448, 0.4544),(0.7079, 0.2920), (0.6427, 0.2905) and (0.4794, 0.4633) based on the CIE1931 color chromaticity diagram, and the green light emitted from thegreen phosphor has a color coordinate falling within a space defined byfour coordinate points (0.1270, 0.8037), (0.4117, 0.5861), (0.4197,0.5316) and (0.2555, 0.5030) based on the CIE 1931 color chromaticitydiagram.
 8. The white light source module of claim 7, wherein the bluelight emitting diode chip has a full width at half-maximum of 10 to 30nm, the green phosphor has a full width at half-maximum of 30 to 100 nmand the red phosphor has a full width at half-maximum of 50 to 200 nm.9. The white light source module of claim 7, wherein the red phosphorcomprises at least one of CaAlSiN₃:Eu and (Ca,Sr)S:Eu.
 10. The whitelight source module of claim 7, wherein the green phosphor comprises atleast one of A₂SiO₄:Eu, SrGa₂S₄:Eu and β-SiAlON, wherein A in A₂SiO₄:Eucomprises at least one of Ba, Sr and Ca.
 11. The white light sourcemodule of claim 7, further comprising a resin encapsulant encapsulatingthe blue light emitting diode chip, wherein the blue light emittingdiode chip is directly mounted on the circuit board.
 12. The white lightsource module of claim 7, further comprising a package body mounted onthe circuit board, the package body defining a reflective cup, whereinthe blue light emitting diode chip is mounted in the reflective cupdefined by the package body.
 13. The white light source module of claim12, further comprising a resin encapsulant formed inside the reflectivecup defined by the package body, the encapsulant encapsulating the bluelight emitting diode chip.
 14. The white light source module of claim 7,further comprising a resin encapsulant encapsulating the blue lightemitting diode chip, wherein the green phosphor and the red phosphor aredispersed in the resin encapsulant.
 15. The white light source module ofclaim 7, further comprising a resin encapsulant encapsulating the bluelight emitting device chip, wherein a first phosphor film comprising oneof the green and red phosphors is formed along a surface of the bluelight emitting diode chip between the blue light emitting diode chip andthe resin encapsulant, and a second phosphor film comprising the otherone of the green and red phosphors is formed on the resin encapsulant.